The broad goal of this study is to increase scientific knowledge of the demographic characteristics and behavioral patterns of female prostitutes, especially as they bear on the heterosexual transmission of AIDS and other sexually transmitted diseases (STDs). Specific aims include (1) developing empirically-based estimated of the size and composition of the female prostitute population in a large metropolitan area (Los Angels County); (2) determining the prevalence of infection with human immunodeficiency virus (HIV) and other STDs in this population; and (3) measuring the prevalence of sexual and drug-related behaviors that can transmit or help prevent transmission of HIV. The study will employ a combination of list sampling and area probability sampling. Prostitutes will be randomly sampled from frames that correspond to different modes of solicitation, history of employment in prostitution and other jobs, numbers of clients and their general characteristics, nature of sexual acts performed and precautions taken with clients and nonpaying sexual partners, history of intravenous drug use and needle sharing, history of sexually transmitted diseases, and knowledge and beliefs regarding AIDS and AIDS transmission and prevention. Blood samples will be analyzed for presence of antibodies to HIV-, HTLV-1, and hepatitis B (surface antibodies). Syphilis serology will be performed. Sample observations will be weighted by the inverse of their sampling probabilities and the results summed to arrive at estimated of the size and composition of the prostitute population. HIV antibody status and the prevalence of high risk behaviors will be evaluated for this population and for various subpopulations defined by mode of solicitation (street prostitutes, call girls, etc.). Observations will be further weighted by reported frequency of unprotected acts of sexual intercourse to characterize risk to heterosexual male clients. Multivariate analyses will be carried out to estimate the relationship between seropositivity on the one hand and background variables and risk behaviors on the other. Techniques of survival analysis will be applied to prostitutes' detailed employment histories to analyze patterns of career transition.